Parasitism

Parasitism

• One organism lives off another
• Parasite
• The organism that lives off another
• Host
• The organism being parasitized
• Infection
• When a host has parasites
• Disease
• The outcome of an infection; host usually doesn't die due to the parasite. Typically due to a secondary infection/condition: HIV, AIDS, Host pneumonia

Parasitism continued

• Obligate parasites
• Require a host (Flea, malaria, botfly larvae, athletes foot)
• Facultative parasite
• does better with a host
• Hemiparasites
• Only get some nutrients from their host (mistletoe)
• Microparasites
• small size--> viruses, bacteria, protozoans (malaria)
• Macroparasites
• Large size--> fungi, plants, animals (mistletoe, flea, athletes foot)
• Endoparasites
• Live in the organism; can spend some time outside (botfly larvae, malaria, athletes foot)
• Ectoparasites
• Live on the outside of the organism (flea)

Transmission

• Direct transmission
• transfer from one host to another by direct or indirect contact; no alternate host
• Direct--> round worm
• Indirect--> lice
• Abiotic vectors
• wind, water, especially important in fungal parasites
• Biotic vectors
• The organism transfers the parasite from one organism to another
• Ex: mosquitos carry malaria, zika, etc

Lifecycle are complex and can require...

• Several hosts
• Definitive hosts

Several hosts

• Intermediate or alternate host
• An organism that helps to complete the life cycle of a parasite
• Definitive host
• Where parasites become an adult

Meningeal worm

• Definitive host:White tailed deer, elk, moose
• --->Adult worms live in the meninges of definitive host membranes surrounding brain and spinal cord
• ---> Adults lay eggs that travel through the venous system to the lungs
• ---> The eggs hatch in the lung tissue and become larval stage 1
• ---> The larvae are coughed out of the lungs and are swallowed, then passed in the feces
• ---> Snails and slugs come in contact with the feces and larvae enter the snail and slugs
• Alternate host:
• --->Larvae develop to larval stage 2 (the repeating stage) and to larval stage 3 (infective stage)
• ---> Larval stage 3 infected snails are eaten by deer, elk, moose
• ---> In the abomasum, larvae burrow through the lining and migrate to the meninges

Hosts respond to infection

• Coevolution
• Habitat selection
• Grooming
• Inflammatory response (in animals)

Habitat selection

• Live where parasites are limited
• EX: Deer in shade, deer flies like warm air

Grooming

• Rid themselves of ectoparasites
• Self-grooming--> cleaning of self
• Group grooming--> clean each other
• Birds--> parrots
• Primates--> chimps
• Ant colony--> cordyceps parasite

Inflammatory response (in animals)

• Death or injury of cell
• causes the release of histamine
• histamine causes increased blood flow to the area
• increased blood flow brings in:
• white blood cells
• other immune cells
• antibodies
• scabs form to prevent further infection
• cysts can form to encapsulate the parasite
• ---some parasites form a cyst (scar tissue) to hide from the immune system; they can remerge at another time

Inflammatory response (in plants)

• Cyst and scab formation (not like in animals/humans)
• cut off infected tissue from healthy tissue; tissue dies
• Gall formation
• Encapsulate parasite (more similar to cyst in animal)
• often marked for predation by others by shape OR color
• Pitching out
• Conifer defense (pitch)
• Response to parasite burrowing into tree; Pine bark beetle

Parasites impact host survival and repro.

• Parasite loads reduce survivability
• ---sheep lung worm & big horn sheep--> 80% mortality
• parasites change behavior of host; increase infection
• parasites loads reduce reproduction
• parasites can regulate populations; prickly pear vs. cactus moth
• European hares and myxoma (virus)
• mosquito vector in order to pass virus
• In 1950-->99.9% kill rate
• In 1953-->95% kill rate
• In 1980-->50% kill rate
• Less virulent--> takes longer to kill; greater viral spread
• Immunity of population--> more rabbits survive = coevolution

Parasite load

• The percent of infected hosts or the quantity of parasites that a host carries
• Parasite load increases with:
• Density of population (ease of transmission)
• Age of the population (depressing of the immune system)
• Note:Symbiosis vs Mutualism
• Symbiosis:
• Obligatory mutualism
• Mutualism:
• Both benefit (facultative)

Mutualism

• Parasitism is the source of mutualism
• Nutrient gathering
• Ruminant and hindgut fermentors
• bacteria and plants---> N fixation<--->cysts
• Mycorrhizae ---> fungi and plants; water and mineral absorption
• Lichens---> fungi and algae
• Flower pot plant and ants (root in leaf)
• Corals, jellyfish, clams, and algae
• Seed dispersal
• Pollination